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  Method and system for frequency drift predictionThe Patent Description & Claims data below is from USPTO Patent Application 20060055595. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates generally to the field of communications, and more particularly to a method and system for providing an improved frequency drift prediction scheme. BACKGROUND OF THE INVENTION [0002] Frequency drift as a result of thermal activity in a cell phone essentially affects all Global Positioning System (GPS) enabled cellular phones and their ability to quickly provide a location fix. Accurately predicting frequency drift rate in parts per million per second (ppm/sec) or parts per billion per second (ppb/sec) is difficult in a typical application due to dynamic signal conditions in a real life environment and the different rates of change of temperature experienced by the phone. The thermal factors typically experienced by a phone can be heavily dependent on ambient temperature, phone temperature, phone transmitter power, relative placement of the crystal (XTAL) or temperature corrected crystal oscillator (TCXO) to the heat generating components in the layout, charger activity, phone mode of operation (emergency call, idle, packet data, etc). Typically, an assumption is made by the software in the phone that accounts for the worst possible thermal drift rate. This assumption leads to longer GPS time to first fix (TTFF) times as the frequency search algorithms must be wide enough to account for these worst case conditions. [0003] Several companies discuss the use of Automatic Frequency Control (AFC) from the cell phone system to provide either a one time assist to the GPS engine or a continuous correction. No existing phone tries to predict or estimate frequency drift rate and drift rate uncertainty of the reference oscillator in the phone. As mentioned above, this drift rate will be different depending on the environmental and phone state. SUMMARY OF THE INVENTION [0004] Embodiments in accordance with the present invention can provide a method by which the uncertainty in both frequency error and frequency drift rate can be narrowed considerably by a simple method of running averages. In this fashion, the phone's AFC (whose variation spreads under bad signal quality conditions in the downlink and improves under better conditions) is used in real-time to determine the frequency error, frequency drift rate and frequency drift rate uncertainty. The algorithm can be used on any cell phone application regardless of the temperature characteristics of the reference oscillator. [0005] In a first embodiment of the present invention, a method of frequency drift prediction for use by a positioning receiver can include the steps of determining estimates for a frequency error, a frequency drift rate, and a frequency drift uncertainty in a communication device based on moving averages and then providing the frequency error, the frequency drift rate and the frequency drift rate uncertainty to the positioning receiver. The step of determining the frequency drift rate can include the step of measuring a running average of a frequency error. Then a point-to-point slope can be calculated from this running average of the frequency error for a predetermined time period. The method can further include the step of determining a moving average of the point-to-point slope in a communication device. The method can further include the steps of determining a frequency drift rate uncertainty window from the difference between maximum and minimum of the drift rate. The positioning receiver can be a global positioning receiver and the step of providing frequency error, drift rate, and drift rate uncertainty can occur when the global positioning receiver is in a weak satellite signal condition. Optionally, the steps of determining the drift rate and the drift rate uncertainty is done using the automatic frequency control of the communication device in real-time. Using the method described above, a time-to-first-fix can be accelerated for the positioning receiver at weak satellite signal levels where dwell times are typically elongated and the wide frequency search windows degrade TTFF considerably. [0006] In a second embodiment of the present invention, another method for generating a frequency reference in a hybrid communications device can include the steps of generating a clock signal at a base frequency, performing communications processing in a communications receiver based on an input of the clock signal at the base frequency; and generating frequency tracking data containing frequency error, frequency drift rate and a frequency drift rate uncertainty of the communications receiver. The method can further include the steps of performing positioning processing in a positioning receiver based on an input of the clock signal at the base frequency and transmitting a control message to the positioning receiver to adapt positioning processing based on the frequency tracking data. The frequency tracking data can include an automatic frequency control message. [0007] In a third embodiment of the present invention, a system for generating a frequency reference in a hybrid communications device, can include a clock source generating a clock signal at a base frequency and a communications receiver that performs communications processing based on an input of the clock signal at the base frequency and generates frequency tracking data containing an offset frequency (or frequency error), a frequency drift rate, and a frequency drift rate uncertainty. The system can further include a positioning receiver that performs positioning processing based on an input of the clock signal at the base frequency and a processor that communicates with the communications receiver and the positioning receiver and transmits a control message to the positioning receiver to adapt positioning processing based on the frequency tracking data. The communications receiver can be a cellular telephone, a personal digital assistant, a messaging device, a two-way pager, a radio receiving device, a modem, a network-enabled wireless device, a radio receiving device, a transceiver, a wireless modem, a wired modem or an optical-receiver. The positioning receiver can be a GPS receiver. The frequency tracking data can be an automatic frequency control (AFC) message which can contain frequency deviation data generated by comparison to a base station signal. [0008] Other embodiments, when configured in accordance with the inventive arrangements disclosed herein, can include a system for performing the methods disclosed herein and a machine readable storage for causing a machine to perform the various processes and methods disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1 is a block diagram of a system for frequency drift prediction in a mobile radio in accordance with an embodiment of the present invention. [0010] FIG. 2 is a flow chart illustrating a method of frequency drift prediction for use by a positioning receiver in accordance with an embodiment of the present invention. [0011] FIG. 3 is a flow chart illustrating another method of generating a frequency reference in a hybrid communications device in accordance with an embodiment of the present invention DETAILED DESCRIPTION OF THE DRAWINGS [0012] While the specification concludes with claims defining the features of embodiments of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the figures, in which like reference numerals are carried forward. [0013] Embodiments in accordance with the present invention can provide a method by which the uncertainty in both frequency error and frequency drift rate can be narrowed considerably by a simple method of running averages. In this fashion, the phone's AFC (whose variation spreads under bad signal quality conditions in the downlink and improves under better conditions) can be used in real time to determine drift rate and drift rate uncertainty. [0014] An architecture or system 100 in which a frequency management system according to the invention may be implemented is illustrated in FIG. 1, in which a combined communications/positioning device incorporates both GPS receiver circuitry 106 and a communications transceiver 104. As illustrated, the communications transceiver 104 may include a receiver front end 136 for detection and downconversion of communications carrier signals, such as cellular telephone or other radio frequency (RF) or other signals, as well as a baseband receiver 138 for processing downconverted communications signals. The communications transceiver 104 of the combined device may be or include for instance a portable radio, cellular telephone, two-way or other pager, wireless modem, wireless personal digital assistant or other device that receives or transmits a radio, optical or other wireless communications signal. In embodiments, the communications transceiver 104 may communicate with or receive signals from a base station 108, such as a cellular base station, or other communications facility or site. [0015] The combined communications/positioning device as illustrated may contain a base oscillator 102 to provide a frequency reference to ultimately drive the communications transceiver 104 as well as the GPS receiver circuitry 106. In embodiments base oscillator 102 may be a free-running, uncompensated reference part. The base frequency of the base oscillator 102 may be set to values compatible with cellular or other operation at 800/900 MHz, 1900 MHz or other frequency ranges. The base oscillator 102 may for example be set to 16.8 MHz or other frequencies which may be multiplied to carrier ranges. An uncompensated crystal oscillator used to implement base oscillator 102 may by itself typically exhibit, for instance, a frequency deviation of .+-.3 ppm or more or less. In other implementations, the base oscillator 102 can be or can include a TCXO or other compensated part achieving tighter or better frequency tolerance. [0016] The base oscillator 102 as illustrated can deliver a frequency reference to a first phase locked loop 110 to drive operating frequencies for cellular or other communications or other operations. The first phase locked loop 110 can include a phase comparator 112, to compare the phase of the base oscillator 102 with the phase of a high-frequency oscillator 116. High-frequency oscillator 116 can for instance be implemented as a voltage controlled high-frequency oscillator (VCO) generating frequencies, for instance, in the 800/900 MHz, 1900 MHz or other ranges for cellular or other operation. A loop filter 114 may low-pass filter the output of the phase comparator 112 to remove higher frequency artifacts or other noise, and stabilize the phase locked loop 110. [0017] The output of the loop filter 114 may in turn drive the high-frequency oscillator 116 to operating frequencies, which through the return provided by loop divider 118 completes a closed feedback loop to phase comparator 112. The phase of the high-frequency oscillator 116 is thereby locked to the phase of the base oscillator 102, so that the phase angle between them remains zero or approximately zero, or at a fixed or approximately fixed separation during operation. [0018] The clock reference of the high-frequency oscillator 116 forms an output of the first phase locked loop 110, which can in turn drive communications transceiver 104 to demodulate, downconvert and receive the wireless signals broadcast to the communications device, or perform other communications operations. According to one embodiment, the frequency reference of high-frequency oscillator 116 can be programmed or scaled according to operating needs, such as for instance for multi-band operation for cellular handsets, or other implementations. [0019] The communications transceiver 104 may acquire and lock to base station 108, such as a cellular base station, or other communications sites or networks. Once registered to base station 108, the communications transceiver 104 can measure the degree of frequency offset (or frequency error) between the output of the first phase locked loop 110 driving the communications transceiver 104, and the base station 108. The frequency offset may be tracked to a fairly high accuracy, for instance .+-.0.1 ppm or more or less, in part because cellular or other base stations 108 may maintain accurate cesium or other clock references which may be broadcast over their communications channels. In accordance with one embodiment, frequency error, drift rate, and a drift rate uncertainty estimates can be determined. In this regard, a running average of an instantaneous frequency error can be calculated and a point-to-point slope can be determined from the running average of the instantaneous frequency error to provide an instantaneous drift rate. Thus, for a predetermined time period (most likely determined or based on the transmission slot scheme used by a particular communication system), a running average of the point-to-point slope of frequency error can be determined as the estimate of drift rate. Furthermore, a drift rate uncertainty is determined from the drift rate as the difference between maximum and minimum from a predetermined time period. Continue reading... Full patent description for Method and system for frequency drift prediction Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and system for frequency drift prediction patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Method and system for frequency drift prediction or other areas of interest. ### Previous Patent Application: Radar apparatus Next Patent Application: Satellite-based positioning system improvement Industry Class: Communications: directive radio wave systems and devices (e.g., radar, radio navigation) ### FreshPatents.com Support Thank you for viewing the Method and system for frequency drift prediction patent info. IP-related news and info Results in 0.1114 seconds Other interesting Feshpatents.com categories: Tyco , Unilever , Warner-lambert , 3m |
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